Man like you I cannot hear the progression. Did notice that they kind of lean heavy on a C E7 F G progression in some of their music and that may be a common pattern in that genre. I would look up tunes similar and note the most common key signatures, and mess around with them to see if something clicks.
I might be that the key is fixed by the fiddle that is dominant to their music..... sorry I can't be more helpful.
Take Care, and Welcome to Chordie!!